The present invention relates to an image printing system, more precisely relates to an image printing system, in which image data of an original image on a printing plate are inputted and amount of ink of an offset printing machine is properly controlled to print the image on a sheet-shaped medium.
Conventional methods and devices for setting amount of ink of offset printing machines have been disclosed in some documents, e.g., Japanese Patent Gazettes No. 8-11292, No. 11-115159. For example, in the Japanese Patent Gazettes No.8-11292, an ink preset device, which is capable of presetting amount of ink to be supplied, is disclosed. In the ink preset device, an image on a printing plate is read by an image scanner, and the scanned image data are stored in a server. The server has: an ink clearance correcting value table, which includes values for correcting ink clearance, which defines amount of ink, on the basis of kinds of ink; and a mechanical correcting value table, which includes values for correcting mechanical conditions on the basis of types of printing machines, etc. The server calculates rate of area of picture in each segment on the basis of the scanned image data. Then, the server selects proper correcting values, from the ink clearance correcting value table and the mechanical correcting value table, on the basis of the rate of area of picture. To properly adjust the ink clearance, an end section of a film blade, which defines the amount of ink, is machined. For example, a plurality of slits, which have proper separations and length, are formed in the end section of the film blade, or each part of the film blade, which corresponds to each segment, is partially cut. In the case of employing divided blades, the amount of ink is defined by ink clearance adjusting units, which respectively correspond to the segments.
In the Japanese Patent Gazettes No. 11-115159, an ink blade adjusting unit, which is capable of easily precisely adjusting a zero point of an ink blade, is disclosed. The ink blade adjusting unit includes: an ink tank; an ink supply roller; a plurality of divided ink blades, which are arranged in an axial direction of the ink supply roller; a detection unit, which detects if front ends of the blades contact an outer circumferential face of the ink supply roller or not; and a control unit for controlling motors, etc. on the basis of signals from the detection unit. When detection signal is sent from the detection unit to the control unit, the control unit controls the motor, etc. so as to adjust the amount of ink by adjusting the ink clearance, which is a space between the front ends of the ink blades and the outer circumferential face of the ink supply roller.
However, in the ink preset device disclosed in the Japanese Patent Gazette No. 8-11292, the slits must be formed in the film blade or the film blade must be partially cut on the basis of the data of the corrected ink clearance. The rate of area of picture is stored in the server, so the same film blade can be manufactured without re-scanning a printing plate. But the film blade must be machined every time so as to define the proper ink clearance. Therefore, it takes a long time to manufacture the film blade, and manufacturing cost of the film blade must be high. Especially, in the case of a color printing machine, four film blades for colors of magenta, cyanogen, yellow and black must be required, so manufacturing time must be longer.
In the case of the divided blades, the zero points of the divided blades may be adjusted by the ink blade adjusting units, but a standard width of the ink clearance must be manually adjusted on the basis of perception of a skilled operator. Therefore, it is difficult for unskilled operators to properly adjust the ink clearance. Especially, in the case of a color printing machine, the ink clearance for each color must be adjusted, so it takes a long time to adjust the ink clearance of the blades.
Further, the ink blade adjusting unit, which is disclosed in the Japanese Patent Gazette No. 11-115159, detects if front ends of the divided ink blades contact the ink supply roller or not so as to adjust the zero point. And, the ink blade adjusting unit drives the motor, etc. so as to move the ink blades, so that the ink clearance between the front ends of the ink blades and the ink supply roller can be adjusted. However, it is difficult to mechanically adjust the ink clearance. Namely, many factors, e.g., kinds of inks, temperature, humidity, influence to the amount of ink supplied through the ink clearance. Thus, the ink clearance must be adjusted on the basis of perception of a skilled operator. It is difficult for unskilled operators to properly adjust the ink clearance. Especially, in the case of a color printing machine, many points to be adjusted exist, so working efficiency must be lower. Further, if the ink blade adjusting unit is provided in the vicinity of the ink tank, the printing machine must be bigger and manufacturing cost of the printing machine must be increased.
An object of the present invention is to provide an image printing system, which is capable of solving the above described disadvantages of the conventional systems and properly defining the amount of ink without adjusting the ink clearance.
To achieve the object, the present invention has following structures.
The image printing system of the present invention comprises:
means for inputting image data of an original image on a printing plate;
an offset printing machine, in which proper amount of ink is supplied from an ink tank to a plate drum via an ink fountain roller on the basis of the image data so as to form an ink image on the plate drum, the ink image is transferred from the plate drum to a blanket drum, then the ink image is transferred onto a sheet-shaped medium, which is conveyed to a space between the blanket drum and a press drum;
memory means for storing the image data inputted by the inputting means, the memory means storing an ink amount table, in which rotational speed data of the ink fountain roller corresponds to rate of area of picture in the original image;
control means for calculating the rate of area of picture on the basis of the image data, reading the rotational speed of the ink fountain roller from the ink amount table on the basis of the rate of area of the picture, correcting the rotational speed so as to define proper control data for rotating the ink fountain roller, and sending the proper control data to the offset printing machine so as to control the amount of ink to be supplied to the plate drum.
In the image printing system, the memory means may further store a correcting value table, which includes values for correcting the rotational speed of the ink fountain roller on the basis of parameters, such as a kind of the ink, settings for printing; and
the control means may further read the correcting value from the correcting value table and defines the proper rotational speed of the ink fountain roller.
In the image printing system, the offset printing machine may be provided to a bottom part of the ink tank and have a scraper, whose front end is located close to an outer circumferential face of the ink fountain roller, and
the control means may control the rotational speed of the ink fountain roller without changing a position of the scraper.
The image printing system may further comprise means for adjusting a clearance between the scraper and the ink fountain roller.
In the image printing system of the present invention, the amount of ink is not controlled by adjusting the ink clearance, which is mainly controlled by perception of an operator in the conventional systems. The amount of ink is controlled by adjusting the rotational speed of the ink fountain roller, so that the system can be easily operated. And, the proper amount of ink can be quickly defined, so that printing efficiency can be improved.
Unlike the conventional systems, machining a film blade and adjusting the ink clearance of each segment are not required. Therefore, the image printing system of the present invention can be easily operated. Further, no ink blade adjusting unit is required, so manufacturing cost of the system can be reduced and the offset printing machine of the system can be smaller.
If means for adjusting the clearance between the scraper and the ink fountain roller is provided, the clearance can be precisely adjusted on the basis of light and shade of the image data without perception of an operator.